This invention relates generally to a security device. In particular, the present invention relates to an anti-theft security device and alarm system.
Security devices are a part of doing business today. The low cost and obvious benefit of anti-theft measures make them used even on objects of small value in department and retail stores. However, rare objects and collectibles are often found unprotected in today's marketplace. This is partly the result of the decentralized nature of the antique business, trade shows, festivals, and similarly operated businesses in which there are many operators of independent booths in a single area. An anti-theft measure addressing the needs of decentralized merchants would be a welcome addition to their professions. Specifically, an alarm system is needed that provides warning when a dealer's property is moved.
Many stores utilize AM (acousto-magnetic) tags. Wide entrances can be covered, and the tags themselves are inexpensive. A transmitter is set near the area to be monitored (usually on one side of the store's door) and sends out intermittent pulses of radio waves. The material the tag is made of actually expands and contracts in size in the presence of this radio field. If the transmitter is operating at the correct frequency, the tag resonates like a tuning fork and produces a radiated signal that continues in between the pulses of radio waves. A receiver set to correspond to the transmitter (usually on the opposite side of the store's door, so that everything must pass between the transmitter and receiver when leaving) listens for this vibration to sense a tag. This system cannot distinguish multiple tags, however, and is poorly suited for monitoring multiple booths or areas without tightly controlled exits.
The most commonly used anti-theft systems in stores are swept-RF systems, mostly due to their extremely low cost. In these systems, a tag is little more than a simple transmitter circuit and a flexible aluminum antennae printed on a paper backing. When an item is purchased, a high-energy burst of radio energy is delivered in close proximity to the tag. This burns out the circuitry and deactivates the tag. Receivers are positioned at the stores' exits to detect active tags. However, like the AM systems described above, swept-RF is unable to distinguish multiple tags. It also suffers from being poorly suited for monitoring multiple booths or areas without tightly controlled exits.
The fastest rising trend in security products is RFID (Radio Frequency Identification). Essentially, a stationary reader sends out a radio signal of a particular frequency. The tag responds to this signal by “replying” in a way that alerts the reader that a tag has just entered its range. This information can then be used to draw conclusions about the location of the tagged object. If a theft is suspected, an alarm can be triggered. In passive RFID systems, the tag does not require a battery. Instead, the energy of the reader signal provides the energy necessary to reply. The circuitry required is exceedingly small—not much bigger than a grain of rice. These devices can also be very unobtrusive and have lengthy life-spans. The largest disadvantage of passive systems is that the reader must provide a powerful transmission in order to power the tag. This results in large power requirements and limits the signal range. Generally the tag must be within a few feet of the reader to be “seen”.
Active RFID systems are powered by a battery onboard the tag. When the tag detects the reader signal, it transmits a reply. Some active systems have a range of hundreds of feet, but more importantly multiple tags can be identified simultaneously. The tag can also respond independently of the reader, such as activating if an attempt is made to disable it. Both passive and active RFID systems in the current state of the art rely on detecting the presence of a tag near an exit to activate an alarm.
Various proposals for other theft alarm devices are found in the art. U.S. Pat. No. 4,584,571 discloses attaching a permanent magnetic body to a valuable article that is placed in a bag. The bag includes circuitry that sets off an alarm when the magnet is missing unless manually overridden.
U.S. Pat. No. 5,963,131 discloses using a motion sensor in combination with a proximity sensor to guard valuables and reduce incidences of false alarms. A theft detector unit is integrated into a laptop, and a control unit is carried by the user to maintain two-way communication with the laptop.
U.S. Pat. No. 6,172,607 discloses an alarm that is attached to an object and manually activated. When the object is thereafter moved, an alarm sounds until disarmed by entering a security code or the internal power source is exhausted. Thus, the alarm detects its own movement, and no corresponding device is used.
While assumably effective for their intended purposes, none of the above proposals provide an anti-theft alarm system that addresses the needs of decentralized merchants. Therefore, it is desirable to have a security device and alarm system that is unobtrusive, can be used in a variety of settings, is able to monitor and distinguish between multiple objects, alerts the merchant when the device is turned off, and is inexpensive.